1. Field of the Invention
The present invention relates to a method for manufacturing an optical disc apparatus and the optical disc apparatus each capable of using a recordable (or re-writable) optical disc as a medium and, more specifically, to a method for manufacturing an optical disc apparatus and the optical disc apparatus suitable for reducing the influence of characteristic variations of circuits.
2. Description of the Related Art
In recent years, an optical disc apparatus using various recordable (or re-writable) optical discs (CD and DVD) as media has been used in various applications. For example, for a CD-R (compact disc-recordable) as an example of the recordable optical disc, a calibration operation is performed in advance using an optical disc to be recorded on so as to allow for writing with appropriate optical power. Detailed contents are described in Orange Book, the specifications of CD-R.
The reason why calibration is required is that writing performed with inappropriate optical power causes a loss in spatial shape balance between land and pit formed by light irradiation. The prior arts relating to calibration include those described in Japanese Patent Laid-open Application No. 2002-100046 (Patent Document 1), Japanese Patent Laid-open Application No. 2003-123299 (Patent Document 2), Japanese Patent Laid-open Application No. 2003-168214 (Patent Document 3), and so on.
Besides, for example, in the case using CD-R as a recordable optical disc, photoelectric conversion of reflected light by an optical pickup head and amplification of an electric signal output after the photoelectric conversion are prerequisitely necessary when reading recorded information. The prior arts relating to processing when reading include those described in Japanese Patent Laid-open Application No. 2000-215610 (Patent Document 4), Japanese Patent Laid-open Application No. Hei 11-213412 (Patent Document 5), Japanese Patent Laid-open Application No. 2003-257030 (Patent Document 6), and so on.
By calibrating the writing optical power, appropriate optical power can be set for the present. The calibration operation, however, includes an operation of reading a predetermined signal which has been written as trial within a calibration area of a medium and obtaining the degree of imbalance between upper and lower parts (β value) of the outputted waveform. In this event, the obtained β value actually includes an offset inherently possessed by a circuit for obtaining a β value. Accordingly, setting of the writing optical power with respect to the β value thus obtained results in setting of the writing optical power offset from a real optimal value. As a result, writing is not optimally performed. Such offset inherently possessed by the circuit is not mentioned in the aforementioned documents.
Besides, for the photoelectric conversion by an optical pickup head and amplification of output after the photoelectric conversion, the photoelectric conversion sensitivity and the amplification gain are designed based on the reflectance of the optical disc so as to obtain a signal at a desired level as a level after amplification. Actually, the signal level after amplification, however, rarely becomes a desired level due to variations in the photoelectric conversion sensitivity and the amplification gain. Therefore, processing for a signal at the desired level cannot be performed, which may cause degradation in read performance. Note that such variations in photoelectric conversion sensitivity and the amplification gain are not mentioned in the aforementioned documents.